Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
The eye is coated by a layer of tear film secreted by the lacrimal gland and distributed over the eye by motion of the eyelids. The tear film layer serves a number of biological functions including to lubricate and protect the corneal surface (epithelium). Dry eye disease, or ocular surface dryness is characterized by irritation of the epithelium and associated discomfort. The condition can be due in part to low aqueous tear flow and/or excess tear fluid evaporation, which results in tear fluid with a relatively elevated solute concentration (i.e., hyperosmolarity). Hyperosmolarity may also be due in part to irregularities in various physiological osmo-regulation and compensatory mechanisms responsible for tear fluid homeostasis. In any event, the increased concentration of solutes in the tear fluid causes irritation of the epithelium, which then leads to compensatory reactions in the eye (e.g., immunological inflammation) due to the epithelial damage.